A US helicopter crash in eastern Afghanistan has killed 31 US special forces and seven Afghan soldiers.

The crash happened on Friday night when the helicopter was taking the soldiers back to their base after an operation.

The Taliban have claimed responsibility, saying their fighters downed the helicopter in a battle with Nato troops, according to the office of the Afghan president, Hamid Karzai. The Islamist group said eight of its fighters had been killed in the fighting.

The incident is believed to be the biggest single loss of life for US forces in Afghanistan since operations began in 2001.

Nawaz Haqyar, a provincial police chief, said the helicopter had come down in Maidan Wardak province, west of the capital, Kabul.